execute subcommand in UNIX with `command`

A subcommand can be exceuted when enclosing it in single backticks (`):
Examples:

mv a `echo b`

List all packages (-qa) containing the name under $PKG and deinstall it (-e option) if only one is returned.

rpm -e `rpm -qa | grep $PKG`

RPM Package unter Red Hat Enterprise Linux entpacken

rpm2cpio my_pkg.rpm | cpio -dimv